The present invention relates to Hall elements, and in particular to Hall elements with offset compensation.
Hall elements make use of the Hall effect, for example, for measuring a magnetic field. The Hall effect is understood to be the occurrence of an electric field perpendicular to the current density vector j as a result of the effect of a magnetic field. The perpendicular electric field E is calculated by the following equation:
E=xe2x88x92R(jxc3x97B).
In this equation, R is the Hall constant. For impurity semiconductors, the Hall constant is proportional to the difference between the mobility of the holes in the semiconductor and the mobility of the electrons in the semiconductor.
Materials having Hall constants that are sufficiently high to be used as substrate or sensor region or simply as a region for a Hall element, are for example intrinsic-conduction InSb, In(AsP), InAs or lightly p- or n-doped regions on silicon. Two contacts are used to conduct an operating current through the region.
In contrast thereto, the two other contacts are used for tapping the Hall voltage formed due to the Lorentz force which leads to deflection of the moving charge carriers due to a magnetic field acting on the Hall element. After a short period of time, there is created an electric field in the Hall element that is directed perpendicularly to the operating current and has such an intensity that the Lorentz force acting on the charge carriers of the operating current is compensated.
The Hall effect or a Hall element, in addition to measuring a magnetic field in accordance with magnitude and sign thereof, may also be utilized for multiplication of two electric quantities, i.e. the magnetic field and the control current, or for contactless signal generators. An additional possibility consists in arranging a Hall element in the vicinity of a conductor track and to measure, in non-contacting manner, the current in this conductor track by detection of the magnetic field generated by the current through said conductor track.
FIG. 5 illustrates a planar Hall element 100, comprising a region 100 formed of a material having a sufficiently high Hall constant. It is to be pointed out that, in the sense of the present description, the region of the Hall element having a non-zero Hall constant may either be a Hall substrate itself, which could be applicable for larger Hall elements, while however the region may also be a portion or region of an integrated circuit which in known manner is embedded in the IC substrate, e.g. in a well, or which has been modified by specific technological steps in order to have a corresponding Hall constant.
The region illustrated in FIG. 5 is of cruciform shape, which affords the advantage that the Hall element shown in FIG. 5 is also suited for so-called spinning current operation, i.e. that the operating current I can be passed through region 100 via contacts K1 and K3, while however in a different mode of operation, the operating current I may also be passed through the region via contacts K2 and K4, with the Hall voltage, of course, being present then at contacts K1 and K3 such that the same can be tapped at terminals A1 and A3. For the following considerations, however, and without restriction to the general nature, it will be assumed for reasons of convenience that the operating current I is applied via terminals A1 and A3, i.e. is fed to and removed from the region via the contacts K1 and K3, while the Hall voltage is given by a potential difference between the contacts K2 and K4, i.e. can be tapped at the terminals A2 and A4.
In addition to a region 100 with a non-zero Hall constant and the contacts K1, K2, K3 and K4 for contacting the region 100, a Hall element of course needs also leads 110, 120, 130 and 140 for electrically connecting the corresponding contacts K1 to K4 to the corresponding terminals A1 to A4. In case of the known Hall element shown in FIG. 5, the leads 110 to 140 are designed in accordance with the practical circumstances. Practical circumstances consist in particular in that there is, for example, the requirement that all terminals A1 to A4 should be arranged closely together in order to be passed, for example, to a central switching unit for spinning current operation. In that case, it is necessary, as shown in FIG. 5, to pass at least one lead, namely lead 130, around the Hall region 100. In other words, lead 130 comprises a first section 130a corresponding to the direction of the current I, a second section 130b perpendicular thereto, as well as a section 130c directed parallel to current I, but having the current flowing therethrough in the direction opposite to the operating current I.
As has already been pointed out, Hall elements serve for measuring an external magnetic field acting on the Hall region. For carrying out such a magnetic field measurement, however, an operating current must be sent through the region so that a Lorentz force can act at all on moving charge carriers. Of course, this operating current I, like any current, also has a magnetic field which also leads to local Hall voltages in the region. However, as the effects of this local intrinsic field are symmetric with respect to the central axis of the current in the element proper, there is no Hall voltage created on the outside of the element, i.e. at the contacts K2 and K4, that could be tapped via the terminals A2 and A4. This local intrinsic field of the operating current I in the Hall region, however, acts in its full magnitude on neighboring Hall elements if arrays of Hall elements are used, as is the case in spinning current operation with mechanical pre-compensation. The intrinsic magnetic field of a Hall element in an array of Hall elements, due to its magnetic field generated and penetrating the neighboring element, leads to a measurement signal there that makes itself felt as an offset. The magnetic field generated by the operating current thus is superimposed on the external magnetic field to be measured in the first place. Thus, there is always an offset problem caused by the magnetic intrinsic field of the active sensor region when there are several sensors provided in the immediate vicinity, since the intrinsic fields of the sensors have the effect of an external magnetic field on the respective other sensors.
An additional problem in the known arrangement shown in FIG. 5 arises due to the terminal leads 110 to 140 which any Hall element needs to have. For connecting the terminals A1 to A4 of the Hall element to a driving control, it is as a rule necessary, as already pointed out hereinbefore, to pass at least one of the current-carrying leads, in the example of FIG. 5 lead 130, around the region 100. In the typical example of the prior art, as shown in FIG. 5, the unfavorable lead from terminal A3 to contact K3 consists of the differently aligned partial lengths 130a to 130c. 
Leads 130a to 130c deliver the following magnetic fields. The magnetic field generated by the operating current flowing through element 130a still is symmetric with the current flow in the active part of the Hall region and therefore generates in region 100 no Hall voltage that is externally measurable. However, this does no longer apply to the two partial lengths 130b and 130c. The magnetic field generated in these conductors acts on the region in its full magnitude and is measured by said region as well, i.e. itself produces a Hall voltage between the terminals A2 and A4. Due to the fact that this additional field is always present when the element is in operation, it appears to the outside like a fixed offset which the element has. Only by changing the operating current is it possible to distinguish this share from a real offset, in that a normal offset changes linearly with the operating current, whereas the offset caused by the operating current due to interference fields changes in square fashion with the operating current.
The document DE 1 019 745 A discloses a magnetic-field dependent resistor assembly and in particular a Hall generator in which a resistor body is of parallelepiped shape having on two opposite narrow sides contacts for supplying an operating current and for removing an operating current, respectively. Each electrode has connected thereto a lead wire extending laterally around the resistor body. In the middle of two other sides of the parallelepiped shape, there are arranged the tapping locations for the Hall voltage, which have lead wires connected thereto. The lead wires are twisted with each other.
U.S. Pat. No. 3,293,586 discloses a Hall plate element comprising a semiconducting material displaying the Hall effect and applied on a layer of mechanically protective, insulating material. Contacts for supplying an operating current are formed by depositing a conductive material in electric contact with the semiconducting material. Furthermore, contacts for tapping the Hall voltage at the semiconducting material are provided by establishing ohmic contact with the semiconducting material. The ohmic contacts have conductive strips connected thereto that extend beyond the semiconducting material, so that contact wires may be soldered thereto.
It is the object of the present invention to provide a Hall element of reduced offset.
In accordance with a first object of the present invention, this object is achieved by a Hall element comprising a region having a non-zero Hall constant; a first contact for supplying an operating current to the region; a third contact for conducting the operating current away from the region, the first and third contacts defining a direction of the operating current within the region; a second and a fourth contact for tapping a Hall voltage; and a conductor pattern connected to the first contact or to the third contact and substantially surrounding the region laterally , the conductor pattern comprising two partial conductors that are connected to the first or the third contact, that are connected to each other and extend, on respective opposite sides of the region, around the region in the direction of the contact to which they are connected, such that an operating current across the contact to which the two partial conductors are connected, can be divided into two operating current shares across the two partial conductors.
In accordance with a second object of the present invention, this object is achieved by a Hall element comprising a region having a non-zero Hall constant; a first contact and a third contact for supplying an operating current to the region and for conducting the operating current away from the region or, optionally, for tapping a Hall voltage; a second and a fourth contact for tapping a Hall voltage or, optionally, for supplying an operating current to the region and conducting the same away from the region; wherein two conductive areas are provided which are both arranged above the region or below the region or are arranged with respect to the region such that one conductive area is arranged above the region and the other conductive area is arranged below the region, wherein the first conductive area is connected to the region in electrically conductive manner in order to form the first contact, with the first conductive area in a contact region of the first contact being moreover electrically isolated from a remainder of the first conductive area; wherein the second conductive area is connected to the region in electrically conductive manner in order to form the third contact, with the first conductive area being not present in a contact region of the third contact, so that the first contact is electrically isolated from the third contact except for the region; wherein the first conductive area is connected to the region in order to form the second contact, with the second conductive area being not present in a contact region of the second contact; and wherein the second conductive area is connected to the region in order to form the fourth contact, with the second conductive area, in a contact region of the fourth contact, being moreover electrically isolated from a remainder of the second conductive area.
The present invention is based on the finding that one has to depart from the opinion valid so far, namely to design the leads merely in accordance with the practical circumstances, but without taking into consideration the operation of the Hall element and the effects thereof on the environment, respectively, in order to provide an offset-reduced Hall element having on the one hand a reduced offset due to its own operating current and having on the other hand also lesser effects on adjacent Hall elements. Although there are presumably methods known in technology for calibrating such offset errors out, it is generally better at all times to not allow such errors to be generated at all, whereby more reliable and less complex and thus less expensive elements may be implemented.
Contrary to the prior art, in which the operating current leads are designed simply in accordance with the external practical circumstances, a Hall element according to the invention has a conductor structure or pattern that is connected to the first or third contact and substantially surrounds the region laterally or is arranged above or below the region. Such a conductor pattern has the effect that the magnetic fields of the current through the Hall element and of a current in the conductor pattern for returning the operating current cancel each other out at least in part in a region outside of the Hall element, i.e. where other Hall elements may be placed, while the magnetic field of the current in the leads at the same time acts on the region as well as symmetrically as possible, so that the magnetic field generated by the current in the conductor pattern, itself does not lead to a Hall voltage in the element. Thus, according to the invention, the intrinsic magnetic field of a Hall element is shielded at least in part from other Hall elements by simple measures, and the additional effect achieved is that the magnetic field of the leads acts at least somewhat symmetrically on the Hall element itself, so that the operating current does not result in a Hall voltage at the element itself.
In a first embodiment of the present invention, the conductor pattern is in the form of a sheet-like metallization above the region so that, analogous with two adjacent flat conductors with different directions of current flow in the interior thereof, i.e. between the region and the metallization plane, an in theory twice as large magnetic field is present tangentially to the surface of the region, whereas the fields perpendicular to the surface as well as all fields outside of the arrangement of region and metallization area are substantially zero or greatly reduced.
Due to the fact that the Hall region can only detect fields extending perpendicularly to the surface, this leads to a considerable reduction of the electric field in the element caused by the intrinsic field.
This metallization area may be arranged either above or below the region, and may have a geometric shape corresponding to that of the region, which provides for high offset freedom, or a shape not corresponding to the geometric shape of the region which, though resulting in reduced offset freedom, already leads to distinct improvements as compared to the prior art.
In accordance with an additional embodiment of the present invention, the conductor pattern for return comprises a first section and a second section which branch in the vicinity of the third contact and are passed around the region preferably symmetrically so as to substantially surround the region. Here too, a shift of the magnetic field in the surroundings of the Hall region takes place so that the magnetic field in the surroundings of the Hall region becomes symmetric to the same and thus does not lead to a Hall voltage. Outside of the return, i.e. in areas where other Hall elements may be placed, there is in contrast thereto just a greatly reduced magnetic field present. This embodiment can be realized more easily in terms of circuit technology since there are no different metallization planes necessary. However, as compared to a second metallization plane as conductor pattern, it has the disadvantage that the offset freedom is not quite as complete.
It may thus be summarized that the conductor pattern according to the invention, due to the fact that it substantially surrounds the region laterally or is arranged above or below the region, at the same time reduces both the interfering influence of the return line on the region as well as the intrinsic field acting on other Hall elements that are arranged in the vicinity.